Voltage Controled Amplifier

[Fleetdog]

I've been thinking recently that it would be cool to have a VCA that I could use with various control voltages to get different effects.  For instance, I could hook it up to an LFO to have a tremolo or to an envelope detector for either a noise gate or slow gear type effect (by slowing the raising edge of the envelope signal).  Has anyone here built something like this?   

[frequencycentral]

Oh yeah!

I've built a quite a few!

There are some choices:

The CA3080 OTA has been used countless times for VCAs. Not production though.

The LM13700 dual OTA can make two VCAs - have a look at the data sheet: http://www.chipcatalog.com/Datasheet/BE374F6E40DD002EAA017C9FA8697817.htm

My current favourite uses a 5672 submini pentode, have a look at the Tube Stereo Panner in http://www.diystompboxes.com/smfforum/index.php?topic=71168.0 - it's uses two 5672 VCAs.

[Paul Perry (Frostwave)]

DIY analog synth people build VCAs all the time, but almost always they are running on +15 and -15V rails (to get best signal/noise, and because that is standard for that kind of gear). Most circuits can be adapted to a single +9 supply though.

Cheapest way to go: (in my opinion) half a LM13700 (see data sheet for circuit). Or you could use a CA3080.
For lowest noise, I expect that Bill on the electro music forum was correct when he said:

"I would think a I think the SSM2164 is by far the best, IMO, VCA chip out there right now and it has four sections or "gain cells" built in. With one SSM2164 IC, you can build 4 LOG VCA's or 2 LIN VCA's since you have to use two gain cells in the feedback path of the other. "

You can make a quiet VCA with a vactrol (led/ldr pair) as well.